Formation of pores in Ge single crystal by laser radiation

Formation of a porous structure on the surface of Ge single crystals by pulsed YAG:Nd laser irradiation at the intensity of 25 MW/cm2 is reported. An increase of surface recombination velocity on the irradiated surface by a factor of 100 is observed and explained by increase of the geometric area of the surface due to formation of pores. The latter is attributed to inhomogeneous pressure of a pulsed laser beam on the melting irradiated surface of the crystal.